Obama says he has high confidence of Syrian chemical weapons use

ST. PETERSBURG, Russia (Reuters) - President Barack Obama told G20 leaders the United States has high confidence that Syrian forces used chemical weapons and underlined the need to uphold an international ban on the use of such weapons, a senior White House adviser said on Friday.

Obama made his case at a lengthy G20 leaders dinner that stretched late into the night on Thursday and was hosted by Russian President Vladimir Putin, the chief opponent to a U.S. push to punish Syrian President Bashar al-Assad over an August 21 chemical weapons attack it blames on his troops.

Ben Rhodes, Obama's deputy national security adviser, told reporters that Obama "once again underscored the very high confidence that we have" that Assad's government launched a poison gas attack that killed 1,429 people.

He made a similar case in talks on Friday with Chinese President Xi Jinping. Both Putin and Xi have blocked U.N. Security Council action against Syria, which has frustrated U.S. efforts for international solidarity.

Obama, who is trying to persuade the U.S. Congress to authorize military force against Syria, told the G20 leaders that it was important to uphold international norms against chemical weapons usage. He noted, however, the paralysis that exists on the Security Council, Rhodes said.